pinctrl: intel: Make use of struct pinfunction and PINCTRL_PINFUNCTION()

Since pin control provides a generic data type and a macro for
the pin function definition, use them in the Intel driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>